磁相变与地壳地球物理异常(英文)

THE MAGNETIC PHASE TRANSITION AND GEOPHYSICAL CRUSTAL ANOMALIES

我们曾提出过一种可能导致地磁和地壳电导率异常的来源:地壳中的二级磁相变,即居里(尼尔)深度附近磁化率的显著提高.这一现象能很好地解释一些来源不明的地磁异常.本文总结了在中地壳深度处、薄且高磁导率异常体的一维和多维大地电磁特征.高磁导率层引起的异常与高电导率层导致的异常相比,大小上可相比拟,但符号相反.无论在什么情况下,经典的大地电磁解释容易导致一个不真实的极厚高阻层,并且在地磁异常附近有与之对应的空间波长,二级磁相变也被认为是这一现象的可能解释.尽管在地壳中是否存在二级磁相变还有一定争议,但最近的一些固体物理实验结果进一步表明它可能是地壳各种地球物理异常的来源之一.

In previous work, we suggested a possible additional source of geomagnetic and crustal conductivity anomalies： the so-called second-order magnetic phase transition in the Eartht s crust, namely a significant enhancement of the magnetic susceptibility near the Curie （Neel） depth. Some geomagnetic anomalies of unknown origin can be easily explained by this phenomenon. In this paper we summarize the one- and multi-dimensional magnetotelluric signatures due to a thin but very high-permeability body at mid-crustal depth. The magnitude of the anomaly due to a high-permeability layer is comparable to that due to a high-conductivity layer, with opposite sign. Wherever the classical magnetotelluric interpretation produces an unrealistic high-resistivity and extremely thick layer, and the nearby geomagnetic anomalies have a suitable spatial wavelength, the second-order magnetic phase transition might be also considered as possible explanation. Although it has been still questionable whether this phenomenon exists in the Earth＇s crust, some recent solid state physics laboratory results make it more and more probable that the magnetic phase transition might be a potential source of various geophysical crustal anomalies.